CONTROL DEVICE OF A SYNCHRONOUS MOTOR

Abstract

Control device (101, 102, 103, 104) of a synchronous motor (60), comprising: a current command generation unit (1) for generating a d-phase current command (I d *) and a q-phase current command (I q *) to generate; a current detection unit (2) for detecting a d-phase current (I d ) and a q-phase current (I q ) to detect; a short-circuit device (3) for short-circuiting the synchronous motor (60) in order to electrodynamically brake the synchronous motor (60); and a short-circuit control unit (4) for controlling the short-circuit device (3), which receives an electrodynamic brake signal, a rotational speed (ω), a speed command (ω*), the d-phase current (I d ) and q-phase current (I q ) and the d-phase current command (I d *) and q-phase current command (I q*), receives, wherein the short-circuit device (3) is provided between an inverter (40) and the synchronous motor (60) and short-circuits terminals of the synchronous motor (60) according to a signal S of the short-circuit control unit (4), wherein the current command generation unit (1) upon receipt of the electrodynamic braking signal generates the q-phase current command (I q *) so that the q-phase current (I q ) is reduced, wherein the short-circuit control unit (4) after receiving the electrodynamic braking signal and after a predetermined time has elapsed from the control of the q-phase current command (I q *) the current command generating unit (1) controls the short-circuit device (3) so that the synchronous motor (60) is short-circuited, and wherein the current command generation unit (1) upon receipt of the electrodynamic braking signal generates the q-phase current command (I q*) so that the q-phase current (I q ) is reduced, and the d-phase current command (I d *) so that the d-phase current (I d ) is increased.

Description

BACKGROUND OF THE INVENTION 1. Field of the invention

[0001] The present invention relates to a control device of a synchronous motor and, more particularly, to a control device of a synchronous motor for preventing demagnetization in the synchronous motor during an electrodynamic braking operation. 2. Description of the state of the art

[0002] Electrodynamic braking is used to perform an emergency stop of a synchronous motor. A brief description of electrodynamic braking will now be given. Fig. 1A shows a connection state between a synchronous motor (hereinafter referred to simply as a "motor") and a drive amplifier during motor driving. A motor 100 is connected to a drive amplifier 200 via power lines 300, so that a current flows through a three-phase coil (not illustrated) of the motor 100. Fig. Figure 1B is a voltage vector diagram illustrated on dq coordinates during operation of the motor, where I d is a d-phase current, I q is a q-phase current, V d is a d-phase voltage, V q is a q-phase voltage, L d is a d-axis inductance, L q is a q-axis inductance, ω is a frequency, K v is a constant of the counter electromotive voltage, and R is a winding resistance.

[0003] When an electrodynamic braking action is carried out, as in Fig. 2A illustrates the motor 100 being separated from the drive amplifier 200, so that the power lines 300 connected to the three-phase coil of the motor 100 are brought into a short-circuited state, and a current caused to flow through the three-phase coil due to an induced voltage of the motor 100 is used as a control current for braking the motor 100. Fig. Figure 2B is a voltage vector diagram illustrated in dq coordinates during electrodynamic braking of the motor. During electrodynamic braking, the voltage across the terminals of the motor 100 becomes zero (0) [V]. Consequently, the q-phase current I flows. q (the torque generation current) which is oppositely directed to generate the counter electromotive voltage K v ω in the motor so that braking occurs.

[0004] At the start of electrodynamic braking, the voltage across the terminals suddenly decreases from a high value to 0 [V]. Therefore, the current amplitude immediately after electrodynamic braking (hereinafter referred to as "DB") begins oscillates. The time-dependent changes in the d-phase current I d and in the q-phase current I q after the start of the DB are in Fig. 3A and Fig. 3B illustrates. Fig. Figure 3A illustrates a case where the initial q-phase current I q immediately after the start of the DB at time 0 [s] is 0 [A]. Fig. Figure 3B illustrates a case where the initial q-phase current I qis large. For convenience, assume that the q-phase current (the torque generation current) accelerates the motor when it is positive in the diagram and decelerates the motor when it is negative. Furthermore, assume that the d-phase current I d (the field weakening current) acts to weaken the field when it is positive.

[0005] As in Fig. 3A illustrates, the d-phase current I d even if the initial q-phase current I q is small, but the current amplitude is relatively small. In contrast, when the initial q-phase current I q is large, as in Fig. 3B, the amplitude of the d-phase current I d larger than when the initial q-phase current I q 0 [A]. In particular, at a time t m Immediately after the start of the DB, the d-phase current I dinstantly increased, so that there is a possibility of causing demagnetization in the permanent magnet used for the rotor of the motor.

[0006] There are methods for suppressing demagnetization caused by electrodynamic braking (for example, as described in JP 5 616 409 B2, JP 2013-99 210 A, and JP 5 113 395 B2, hereinafter referred to as "Patent Documents 1 to 3", respectively). Patent Document 1 discloses a method for controlling a current of a synchronous motor so that the current value of the synchronous motor becomes less than a maximum current value in order to prevent irreversible demagnetization of a permanent magnet, which might be caused by a transient current occurring in the event of a three-phase short circuit. However, there is a problem that the torque is unnecessarily limited because the q-phase current I qis limited in advance to suppress the current.

[0007] Patent Document 2 discloses a motor control device including three switching elements configured to cause a short circuit of three phase coils of a three-phase motor when they are turned on, and to release the short circuit of the three phase coils when they are turned off. When a current flowing through any one of the three phase coils exceeds a predetermined threshold when the three switching elements are in an on-state, the three switching elements are turned off for a first predetermined period of time and turned on after the first predetermined period of time has elapsed. However, since the short circuit of the coils is released after the current of the coils exceeds the predetermined threshold, it is difficult to completely suppress demagnetization due to electrodynamic braking.

[0008] Patent Document 3 discloses an electrodynamic braking device for a motor having the electrodynamic braking device for causing an emergency stop of the motor, wherein, during a predetermined period after the start of an electrodynamic braking operation, control is performed such that an electrodynamic braking current is attenuated through a braking operation with PWM control in which at least a part of the switching elements for controlling the braking current are repeatedly turned on and off, and after the lapse of the predetermined period, control is performed such that an electrodynamic braking current that should have originally flowed flows while all the switching elements are constantly fixed in the on- or off-state without performing the PWM control.However, since the electrodynamic braking current is also controlled to be attenuated after the electrodynamic braking action has started, it is difficult to completely suppress demagnetization due to the electrodynamic braking action.

[0009] DE 10 2013 223 476 A1 discloses a control device for a synchronous motor that aims to enable emergency operation of the synchronous motor while simultaneously preventing demagnetization. The synchronous motor is short-circuited for braking. To prevent abrupt deceleration of the motor, an intermediate range is inserted in which the target torque is gradually reduced to a braking torque at which the motor is then short-circuited. DE 10 2012 223 227 A1 describes devices and methods for generating voltage commands used to control the operation of a permanent magnet machine. Ramp-shaped voltage signals for the d-phase and the q-phase are implemented in a three-phase short-circuit mode to prevent large transient currents that could cause demagnetization. SUMMARY OF THE INVENTION

[0010] Accordingly, it is an object of the present invention to provide a control device of a synchronous motor which enables electrodynamic braking action while avoiding demagnetization of the synchronous motor without excessively limiting the torque.

[0011] The synchronous motor control device according to an embodiment of the present invention includes a current command generation unit for generating a d-phase current command and a q-phase current command; a current detection unit for detecting the d-phase current and the q-phase current; a short-circuit device for short-circuiting a synchronous motor to electrodynamically brake the synchronous motor; and a short-circuit control unit for controlling the short-circuit device. wherein the current command generation unit, upon receiving an electrodynamic braking signal, controls the q-phase current command to reduce the q-phase current, and the short-circuit control unit, upon receiving the electrodynamic braking signal and after a predetermined time elapses from the control of the q-phase current command by the current command generation unit, controls the short-circuit device to short-circuit the synchronous motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The objects, features and advantages of the present invention will become more apparent from the following description of embodiments taken in conjunction with the accompanying drawings, in which Fig. 1A is a view illustrating, in a conventional synchronous motor, a state in which the motor and a drive amplifier are connected during driving of the synchronous motor (the motor); Fig. 1B is a view illustrating, in the conventional synchronous motor, voltage vectors on dq coordinates during driving of the synchronous motor (the motor); Fig. 2A is a view illustrating, in the conventional synchronous motor, a state in which the motor and the drive amplifier are connected during an electrodynamic braking operation of the synchronous motor (the motor); Fig. 2B is a view illustrating, in the conventional synchronous motor, voltage vectors on dq coordinates during the electrodynamic braking operation of the synchronous motor (the motor); Fig. 3A is a view illustrating time-lapse changes of the d-phase and q-phase currents after the electrodynamic braking operation in the conventional synchronous motor when the q-phase current is 0[A] in the initial stage of the electrodynamic braking operation; Fig. 3B is a view illustrating, in the conventional synchronous motor, time-related changes in the d-phase and q-phase currents after the electrodynamic braking action when the q-phase current is large in the initial stage of the electrodynamic braking action; Fig. 4 is a block diagram of a control device of a synchronous motor according to a first embodiment of the present invention; Fig. 5 is a view illustrating changes with time in the d-phase and q-phase currents when the present invention is not applied; Fig. 6 is a view illustrating changes with time in the d-phase and q-phase currents after the electrodynamic braking operation when a reduction in the q-phase current is performed using the control device of the synchronous motor according to the first embodiment of the present invention; Fig. 7 is a view illustrating changes with time in the d-phase and q-phase currents after the electrodynamic braking operation when a decrease in the q-phase current and an increase in the d-phase current are performed using the control device of the synchronous motor according to the first embodiment of the present invention; Fig. 8A is a view illustrating voltage vectors on the dq coordinates before the current phase change; Fig. 8B is a view illustrating voltage vectors on the dq coordinates after the current phase change; Fig. 8C is a view illustrating voltage vectors on the dq coordinates after the current phase change; Fig. 9 is a block diagram of a control device of a synchronous motor according to a second embodiment of the present invention; Fig. 10 is a view illustrating changes with time in the d-phase and q-phase currents after the electrodynamic braking operation when a reduction in the q-phase current is performed using the control device of the synchronous motor according to a third embodiment of the present invention; Fig. 11 is a view illustrating changes with time in the d-phase and q-phase currents after the electrodynamic braking operation when a decrease in the q-phase current and an increase in the d-phase current are performed using the control device of the synchronous motor according to the third embodiment of the present invention; Fig. 12 is a view illustrating changes with time in the d-phase and q-phase currents when the electrodynamic brake is applied after the d-phase and q-phase voltages are brought to 0 [V] using a control device of a synchronous motor according to a fourth embodiment of the present invention; Fig. 13 is a block diagram of a control device of a synchronous motor according to a fifth embodiment of the present invention; Fig. 14 is a block diagram of a control device of a synchronous motor according to a sixth embodiment of the present invention; and Fig. Figure 15 is a view illustrating voltage vectors on the dq coordinates in a transient state after electrodynamic braking. DETAILED DESCRIPTION

[0013] With reference to the drawings, a description will be given below of the control device of the synchronous motor according to embodiments of the present invention. However, it should be noted that the technical scope of the present invention is not limited to the embodiments, but includes the invention set forth in the claims and their equivalents. [First embodiment]

[0014] Referring to the drawings, a control device of a synchronous motor according to a first embodiment of the present invention will be described. Fig. 4 is a block diagram of the control device of the synchronous motor according to the first embodiment of the present invention. As shown in Fig. As illustrated in Figure 4, the control device 101 of the synchronous motor according to the first embodiment includes a current command generation unit 1 for generating a d-phase current command and a q-phase current command; a current detection unit 2 for detecting the d-phase current and the q-phase current; a short-circuit device 3 for short-circuiting a synchronous motor 60 to electrodynamically brake the synchronous motor 60; and a short-circuit control unit 4 for controlling the short-circuit device 3. wherein the current command generation unit 1, upon receiving an electrodynamic braking signal, controls the q-phase current command to reduce the q-phase current, and the short-circuit control unit 4, upon receiving the electrodynamic braking signal and after a predetermined time has elapsed from the control of the q-phase current command by the current command control unit 1, controls the short-circuit device 3 to short-circuit the synchronous motor 60.

[0015] Now the Fig. 4 will be described in detail. A three-phase AC voltage is input from a three-phase AC power supply 10 to a converter 20. The converter 20 converts the three-phase AC voltage into a DC voltage and outputs the DC voltage. The output DC voltage is smoothed by a smoothing capacitor 30 and then input to an inverter 40. The inverter 40 converts the DC voltage via PWM control based on PWM signals V u *, V v * and V w * by a PWM signal generating unit 12 into an alternating voltage with a desired frequency to drive the synchronous motor 60.

[0016] A short-circuit device 3 is provided between the inverter 40 and the synchronous motor 60. The short-circuit device 3 short-circuits terminals of the synchronous motor 60 according to a signal S from the short-circuit control unit 4, thereby performing an electrodynamic braking action.

[0017] A U-phase current I u and a V-phase current I v The three-phase currents supplied to the synchronous motor 60 are respectively detected by a U-phase current detector 4U and a V-phase current detector 4V, and the detection result is output to a current detection unit 2. The current detection unit 2 calculates from the U-phase current I u and the V-phase current I v the d-phase current I d and the q-phase current I q and outputs it to the short-circuit control unit 4 and a voltage command generation unit 5.

[0018] The synchronous motor 60 includes a stator 63 provided with windings of 65U, 65V, and 65W. Furthermore, the synchronous motor 60 includes a rotor 62 rotating around a central axis 61, while magnetic poles 64a to 64d are provided on the inside of the stator 63. The synchronous motor 60 drives a driven body 7.

[0019] Next to the synchronous motor 60, a rotation angle detector 8 is provided, which detects a rotation angle θ of the synchronous motor 60. The rotation angle detector 8 outputs the detection value of the rotation angle θ to the current detection unit 2, the PWM signal generation unit 12, and a rotation speed calculation unit 9. The rotation speed calculation unit 9 calculates a rotation speed ω by differentiating the rotation angle θ with time. The calculated rotation speed ω is output to the short-circuit control unit 4, the torque command generation unit 11, the current command generation unit 14, and the voltage command generation unit 5.

[0020] A host controller 13 outputs a speed command ω* to the torque command generation unit 11 and the short-circuit control unit 4. The torque command generation unit 11 acquires the speed command ω* from the host controller 13 and generates a torque command τ* and outputs it to the current command generation unit 1.

[0021] The current command generation unit 1 generates a d-phase current command I based on the torque command τ* output from the torque command generation unit 11. d * and a q-phase current command I q * and outputs it to the voltage command generation unit 5 and the short-circuit control unit 4.

[0022] The voltage command generation unit 5 generates from the d-phase current command I d * and the q-phase current command I q * a d-phase voltage command V d * and a q-phase voltage command V q* and outputs it to the PWM signal generating unit 12.

[0023] The PWM signal generation unit 12 generates from the d-phase voltage command V d * and the q-phase voltage command V q * PWM signals V u *, V v * and V w * of the corresponding phases and outputs them to the inverter 40.

[0024] The electrodynamic braking signal for stopping the synchronous motor 60 is input to the current command generation unit 1 and the short-circuit control unit 4 from outside the control device 101 of the synchronous motor 60. The present invention is suitably applicable to, but not limited to, an emergency stop where stopping with normal deceleration is not possible. For example, the present invention is also applicable to deceleration during normal operation.

[0025] Now, an advantage of using the control device of the synchronous motor according to the first embodiment of the present invention will be described. Fig. Fig. 5 is a view illustrating changes over time in the d-phase and q-phase currents when the present invention is not applied. Assume that the electrodynamic braking (DB) operation is started at time t0. Before the DB is started, the d-phase current I d and the q-phase current I q constant, whereas these currents become oscillatory after the onset of the DB. The amplitude increases with the q-phase current I q is when the DB is started; when the amplitude of the d-phase current I d large, there is a possibility that demagnetization of the synchronous motor will be caused as described above.

[0026] The control device of the synchronous motor according to the first embodiment of the present invention is configured such that, after receiving the electrodynamic braking signal and after a predetermined time has elapsed from the control of the q-phase current command by the current command generation unit 1, the short-circuit control unit 4 controls the short-circuit device 3 to short-circuit the synchronous motor 30. In other words, it is configured such that the electrodynamic braking operation is performed after receiving the electrodynamic braking signal and after the predetermined time has elapsed from the time the q-phase current command is controlled by the current command generation unit 1, instead of applying the electrodynamic brake immediately upon receiving the electrodynamic braking signal. Fig. 6 is a view illustrating time-lapse changes in the d-phase and q-phase currents after the electrodynamic braking operation when the q-phase current is reduced using the control device of the synchronous motor according to the first embodiment of the present invention. Assume that the current command generation unit 1 and the short-circuit control unit 4 receive the electrodynamic braking signal at time t1. The current command generation unit 1 controls the q-phase current command at time t1 so that the q-phase current I q decreases. Then the q-phase current I q , to and after time t1. The electrodynamic braking action is started at a time t2, at which it is assumed that the q-phase current I qhas decreased sufficiently. As will be understood, the present invention is designed so that the electrodynamic braking action is delayed from the time the electrodynamic braking signal is received, and during this time the q-phase current I q reduced. Consequently, it is possible to detect an increase in the d-phase current I d , which is a field weakening current, thereby avoiding demagnetization of the synchronous motor.

[0027] Now, the fact will be described that it is not always a disadvantage to delay the electrodynamic braking action for the predetermined time as in the present invention, instead of starting the electrodynamic braking action immediately upon receipt of the electrodynamic braking signal. As in Fig. 3A is illustrated at a q-phase current I qin the initial stage of electrodynamic braking action of 0 [A] the q-phase current I q negative and a deceleration moment occurs immediately after the electrodynamic braking action. However, as in Fig. 3B illustrates that at a large q-phase current I q in the initial stage of electrodynamic braking, the q-phase current I q after the electrodynamic braking action is positive for a while, which means that an acceleration torque occurs. Since the q-phase current I q oscillates, the q-phase current I q positive again. Consequently, when the q-phase current I q becomes more oscillating, the time zone that generates an acceleration torque becomes larger. Therefore, in a state where the q-phase current I q is large in the initial stage of electrodynamic braking, a situation may arise in which the q-phase current I qoscillates and accelerates instantly despite the electrodynamic braking action. Consequently, even if the electrodynamic brake is applied immediately upon receipt of the electrodynamic braking signal, it is not always possible to stop the synchronous motor quickly. Given the above, the delay in electrodynamic braking is not always a disadvantage.

[0028] Next, a description will be given of a first modification of the synchronous motor control device according to the first embodiment of the present invention. The first modification is characterized in that, upon receiving the electrodynamic braking signal, the current command generation unit 1 controls the q-phase current command to decrease the q-phase current and also controls the d-phase current command to increase the d-phase current.

[0029] In Fig. 7 is a view illustrating changes over time in the d-phase current and the q-phase current after the electrodynamic braking operation when a decrease in the q-phase current and an increase in the d-phase current are performed using the control device of the synchronous motor according to the first embodiment of the present invention. At a time t3 after receiving the electrodynamic braking signal, the current command generation unit 1 controls the q-phase current command so that the q-phase current I q is reduced, and it also controls the d-phase current command so that the d-phase current I d is increased. Furthermore, at a time t4 after a predetermined time from the receipt of the electrodynamic braking signal, the electrodynamic braking action is started. In this way, by increasing the d-phase current I dpossible to reduce the d-phase voltage and the q-phase voltage directly from the electrodynamic braking action.

[0030] A second modification of the synchronous motor control device according to the first embodiment of the present invention will now be described. The second modification is characterized in that, upon receiving the electrodynamic braking signal, the current command generation unit 1 controls the d-phase current command and the q-phase current command so that the phase of the current flowing in each of the U-phase, the V-phase, and the W-phase is changed in such a direction that the amplitude of the voltage across the terminals of the synchronous motor is reduced.

[0031] In Fig. 8A and Fig. 8B shows views illustrating voltage vectors on the dq coordinates in cases before and after the current phase change, respectively. In Fig. 8A, it should be assumed that the d-phase current and the q-phase current before and after the current phase change are each I d1 and I q1 A current command is generated to shift the phase of the current flowing through each of the U-phase, the V-phase, and the W-phase by θ without changing the magnitude of the command for each of the d-phase current and the q-phase current. Then, the voltage vectors are calculated as shown in Fig. 8B changes and the voltage across the terminals becomes lower than in Fig. 8A. Fig. 8B will Fig. 8C, where the voltage vector across the terminals is the same. After the current phase change, I d1 and I q1 only the obvious d-phase current and q-phase current observed by the control device. In contrast, I d2 the essential d-phase current that contributes to the weakening of the field and is I q2the essential q-phase current contributing to the torque generation, where I d2 > I d1 is, and I q1 > I q2 Thus, it can be seen that even if the electrodynamic braking action is started after the lapse of a predetermined time from the current phase shift, an effect similar to that of the above first modification in which the q-phase current is substantially reduced and the d-phase current is increased can be achieved. For the purpose of illustrating the effect of changing the current phase, a case was described in which the magnitudes of the commands for the d-phase current and the q-phase current are not changed. However, it is possible to change the current phase while changing the magnitudes of the commands for the d-phase current and the q-phase current.

[0032] As described above, in the control device of the synchronous motor according to the first embodiment of the present invention, after receiving the electrodynamic braking signal, the q-phase current I q reduced, and after the predetermined time has elapsed, electrodynamic braking is initiated. This allows electrodynamic braking of the synchronous motor to be performed while avoiding demagnetization of the synchronous motor and without excessively limiting the torque. [Second embodiment]

[0033] Now, a control device of a synchronous motor according to a second embodiment of the present invention will be described using the drawings. Fig. 9 is a block diagram of the control device of the synchronous motor according to the second embodiment of the present invention. As shown in Fig. As illustrated in Figure 9, the control device 102 of the synchronous motor according to the second embodiment of the present invention includes a voltage command generation unit 5 for generating a d-phase voltage command and a q-phase voltage command; a current detection unit 2 for detecting a d-phase current and a q-phase current; a short-circuit device 3 for short-circuiting a synchronous motor 60 to electrodynamically brake the synchronous motor 60; and a short-circuit control unit 4 for controlling the short-circuit device 3; wherein the voltage command generation unit 5 controls the d-phase voltage command and the q-phase voltage command upon receiving an electrodynamic braking signal;and the short-circuit control unit 4, after receiving the electrodynamic brake signal and after a predetermined time has elapsed from the control of the d-phase voltage command and the q-phase voltage command by the voltage command generation unit 5, controls the short-circuit device 3 so that the synchronous motor 60 is short-circuited.;

[0034] The synchronous motor control device 102 according to the second embodiment differs from the synchronous motor control device 1014 according to the first embodiment in the following two points: The first point is that the voltage command generation unit 5 and the short-circuit control unit 4 receive the electrodynamic braking signal. The second point is that the voltage command generation unit 5 controls the d-phase voltage command and the q-phase voltage command after receiving the electrodynamic braking signal, and the short-circuit control unit 4 controls the short-circuit device 3 to short-circuit the synchronous motor 60 after receiving the electrodynamic braking signal and after the predetermined time has elapsed from the control of the d-phase voltage command and the q-phase voltage command by the voltage command generation unit 5.The other structure of the control device 102 of the synchronous motor according to the second embodiment is the same as that of the control device 101 of the synchronous motor according to the first embodiment, and therefore a detailed description thereof is omitted.

[0035] According to the control device of the synchronous motor according to the second embodiment of the present invention, it is configured such that the voltage command generation unit 5, upon receipt of the electrodynamic braking signal, controls the d-phase voltage command and the q-phase voltage command, and the short-circuit control unit 4, upon receipt of the electrodynamic braking signal and after the lapse of the predetermined time from the control of the d-phase voltage command and the q-phase voltage command by the voltage command generation unit 5, controls the short-circuit device 3 so that the synchronous motor 60 is short-circuited. Thus, as in the first embodiment, it is possible to control the q-phase current I qduring electrodynamic braking. Consequently, it is possible to perform electrodynamic braking of the synchronous motor 60 while avoiding demagnetization of the synchronous motor 60 without excessively limiting the torque. [Third Embodiment]

[0036] Next, a description will be given of a control device of a synchronous motor according to a third embodiment of the present invention. The structure of the control device of the synchronous motor according to the third embodiment of the present invention is similar to that of the control device of the synchronous motor according to the first embodiment of the present invention shown in Fig. 4. The control device of the synchronous motor according to the third embodiment of the present invention includes a current command generation unit 1 for generating a d-phase current command and a q-phase current command, a current detection unit 2 for detecting a d-phase current and a q-phase current; a short-circuit device 3 for short-circuiting the synchronous motor 60 to electrodynamically brake the synchronous motor 60; and a short-circuit control unit 4 for controlling the short-circuit device 3. The current command generation unit 1 controls the q-phase current command after receiving the electrodynamic braking signal; and the short-circuit control unit 4, after receiving the electrodynamic braking signal and after the q-phase current reaches a predetermined value, controls the short-circuit device 3 to short-circuit the synchronous motor 60.

[0037] The synchronous motor control device according to the third embodiment differs from the synchronous motor control device according to the first embodiment in that, after receiving the electrodynamic braking signal and after the q-phase current reaches a predetermined value, the short-circuit control unit 4 controls the short-circuit device 3 to short-circuit the synchronous motor 60, rather than the short-circuit control unit 4 controlling the short-circuit device 3 to short-circuit the synchronous motor 60 after receiving the electrodynamic braking signal and after a predetermined time has elapsed from the control of the q-phase current command by the current command generation unit 1. The other configuration of the synchronous motor control device according to the third embodiment is the same as that of the synchronous motor control device according to the first embodiment, and therefore, a detailed description thereof will be omitted.

[0038] In Fig. 10 is a view illustrating time-lapse changes in the d-phase and q-phase currents after the electrodynamic braking operation when the q-phase current is reduced using the control device of the synchronous motor according to the third embodiment of the present invention. Assume that the current command generation unit 1 and the short-circuit control unit 4 have received the electrodynamic braking signal at time t5. The current command generation unit 1 controls the q-phase current command at time t5 so that the q-phase current I q is reduced. Then the q-phase current I q to and after time t5, the q-phase current I decreases and reaches q at a time t6 a predetermined threshold value I qth. If it is determined that the q-phase current I q the threshold I qthhas reached, the short-circuit control unit 4 starts the electrodynamic braking operation at time t6. Thus, in the present invention, the electrodynamic braking operation is started after it has been confirmed that the q-phase current I q the predetermined threshold I qth Consequently, it is possible to detect an increase in the d-phase current I d , which is the field weakening current, thereby avoiding demagnetization of the synchronous motor 60.

[0039] Now, a first modification of the control device of the synchronous motor according to the third embodiment of the present invention will be described. The first modification is characterized in that, after receiving the electrodynamic braking signal, the current command generation unit 1 controls the q-phase current command to decrease the q-phase current and also controls the d-phase current command to increase the d-phase current; and, after receiving the electrodynamic braking signal and after at least one of the q-phase current and the d-phase current reaches a corresponding predetermined value, the short-circuit control unit 4 controls the short-circuit device 3 to short-circuit the synchronous motor 60.

[0040] In Fig. 11 is a view illustrating changes over time in the d-phase and q-phase currents after the electrodynamic braking operation when a decrease in the q-phase current and an increase in the d-phase current are performed using the control device of the synchronous motor according to the third embodiment of the present invention. At time t7, after receiving the electrodynamic braking signal, the current command control unit 1 controls the q-phase current command so that the q-phase current I q is reduced, and it also controls the d-phase current command so that the d-phase current I d is increased. At a time t8, when it is determined by the short-circuit control unit 4 that the q-phase current I q the threshold I qth , which is the predetermined value, the electrodynamic braking action is started. Thus, by increasing the d-phase current I dpossible to reduce the d-phase voltage and the q-phase voltage immediately before the electrodynamic braking operation. The above example illustrates a case where the electrodynamic braking operation is started after confirming that the q-phase current I q the threshold I qth , which is the predetermined threshold value, but is not limited to this. In other words, there may be an embodiment such that the electrodynamic braking action is initiated either after confirmation that the d-phase current I d the threshold I dth has been reached, or after confirmation that both the q-phase current I q as well as the d-phase current I d its threshold value I qth and I dth has been reached, is started.

[0041] A second modification of the synchronous motor control device according to the third embodiment of the present invention will now be described. The second modification is characterized in that the current command generation unit 1, upon receiving the electrodynamic braking signal, controls the d-phase current command and the q-phase current command so that the phase of the current flowing through each of the U-phase, the V-phase, and the W-phase is changed toward a direction in which the amplitude of the voltage across the terminals of the synchronous motor is reduced or toward the direction of the field weakening current; and the short-circuit control unit 4, upon receiving the electrodynamic braking signal and after at least one of the q-phase current and the d-phase current reaches the corresponding predetermined value, controls the short-circuit device 3 so that the synchronous motor 60 is short-circuited.In the second modification, there is such a design that by shifting the phase of the current, the q-phase current I. q is reduced and the d-phase current I d is increased, and the electrodynamic braking action is started after it has been confirmed that at least one of the q-phase current I q and the d-phase current I d the corresponding predetermined threshold value I qth or I dth has been reached; thereby an effect can be obtained which is equal to that of the first modification above.

[0042] As described above, according to the control device of the synchronous motor according to the third embodiment of the present invention, there is such a configuration that the electrodynamic braking operation is started after receiving the electrodynamic braking signal and after confirming that the q-phase current I q the pre-defined threshold I qthhas been reached. This makes it possible to carry out the electrodynamic braking of the synchronous motor while avoiding demagnetization of the synchronous motor and without excessively limiting the torque. [Fourth Embodiment]

[0043] Now, a control device of a synchronous motor according to a fourth embodiment of the present invention will be described. The structure of the control device of the synchronous motor according to the fourth embodiment of the present invention is similar to that of the control device of the synchronous motor according to the second embodiment of the present invention shown in Fig. 9. The control device of the synchronous motor according to the fourth embodiment of the present invention includes a voltage command generation unit 5 for generating a d-phase voltage command and a q-phase voltage command; a current detection unit 2 for detecting a d-phase current and a q-phase current; a short-circuit device 3 for short-circuiting a synchronous motor 60 to electrodynamically brake the synchronous motor 60; and a short-circuit control unit 4 for controlling the short-circuit device 3; wherein the voltage command generation unit 5 controls the d-phase voltage command and the q-phase voltage command upon receiving an electrodynamic braking signal;and the short-circuit control unit 4, after receiving the electrodynamic braking signal and after at least one of the q-phase voltage and the d-phase voltage has reached a corresponding predetermined value, controls the short-circuit device 3 so that the synchronous motor 60 is short-circuited.;

[0044] The control device of the synchronous motor according to the fourth embodiment differs from the control device of the synchronous motor according to the second embodiment in that, after receiving the electrodynamic braking signal and after the q-phase voltage has reached the predetermined value, the short-circuit control unit controls the short-circuit device 3 to short-circuit the synchronous motor 60, instead of the short-circuit control unit 4 controlling the short-circuit device 3 to short-circuit the synchronous motor 60 after receiving the electrodynamic braking signal and after a predetermined time has elapsed from the control of the d-phase voltage command and the q-phase voltage command by the voltage command generation unit 5.The other structure of the control device of the synchronous motor according to the fourth embodiment is the same as that of the control device of the synchronous motor according to the second embodiment, and therefore a detailed description thereof is omitted.

[0045] In Fig. 12 is a view illustrating changes over time in the d-phase current and the q-phase current when the electrodynamic brake is applied after the d-phase voltage and the q-phase voltage are brought to 0 [V] using the control device of the synchronous motor according to the fourth embodiment of the present invention. Fig. 12 illustrates an example in which both the d-phase voltage and the q-phase voltage reach 0 [V], but this is not limited to this. In other words, it may be configured such that the electrodynamic brake is applied when at least one of the q-phase voltage and the d-phase voltage reaches the respective other predetermined value.

[0046] As in Fig. 12 illustrates oscillation of the d-phase current I d and the q-phase current I q not if the electrodynamic braking action is started after the d-phase current I d and the q-phase current I q were regulated so that the q-phase voltage reaches 0 [0]. However, when the d-phase voltage and the q-phase voltage are instantaneously brought to 0 [V] after the electrodynamic braking signal is received, the d-phase current I d and the q-phase current I qsimilar to when the electrodynamic brake is applied instantly. Therefore, it is preferable that the d-phase voltage and the q-phase voltage be brought to an approximation of 0 [V] over a certain period of time (e.g., a few ms). Therefore, in the method of bringing the d-phase voltage and the q-phase voltage to a gradual approximation of 0 [V] by regulating the d-phase voltage command and the q-phase voltage command, what is necessary is that the d-phase voltage V d and the q-phase voltage V q be brought to 0 [V] indiscriminately when the phases of the d-phase current I d and the q-phase current I q be lost. Thus, it is possible to use the synchronous motor control device according to the third embodiment of the present invention even when, for example, the angle detector of the motor malfunctions. [Fifth Embodiment]

[0047] Now, a control device of a synchronous motor according to a fifth embodiment of the present invention will be described. Fig. 13 is a block diagram of the control device of the synchronous motor according to the fifth embodiment of the present invention. As shown in Fig. As illustrated in Figure 13, the control device 103 of the synchronous motor according to the fifth embodiment of the present invention includes a current command generation unit 1 for generating a d-phase current command and a q-phase current command; a current detection unit 2 for detecting a d-phase current and a q-phase current; a short-circuit device 3 for short-circuiting a synchronous motor 60 to electrodynamically brake the synchronous motor 60; a short-circuit control unit 4 for controlling the short-circuit device 3; and a peak current estimation unit 6 for continuously estimating the peak d-phase current based on the detected q-phase current. The current command generation unit 1 controls the q-phase current command so as to reduce the q-phase current after receiving an electrodynamic braking signal.and the short-circuit control unit 2, after receiving the electrodynamic braking signal and after the highest estimated current after electrodynamic braking estimated by the maximum current estimation unit 6 has become less than or equal to a tolerance value, controls the short-circuit unit 3 so that the synchronous motor 60 is short-circuited.;

[0048] As in Fig. As illustrated in Figure 5, if the short-circuit control unit 4 starts the electrodynamic braking action immediately upon receiving the electrodynamic braking signal, the d-phase current may be increased to a level that causes demagnetization of the synchronous motor 60. Therefore, after receiving the electrodynamic braking signal, the current command generation unit 1 controls the q-phase current command to reduce the q-phase current. The highest d-phase current after the electrodynamic braking action can be estimated based on the q-phase current during the electrodynamic braking action.Therefore, in the synchronous motor control device according to the fifth embodiment of the present invention, the peak current estimation unit 6 continuously estimates the peak d-phase current based on the detected value of the q-phase current, and the short-circuit control unit starts the electrodynamic braking action after receiving the electrodynamic braking signal and after the peak estimated current after electrodynamic braking estimated by the peak current estimation unit 6 becomes less than or equal to the tolerance value. In this way, it is possible to appropriately determine the time for which the electrodynamic braking action is delayed depending on the detected value of the q-phase current, so that it is possible to quickly stop the synchronous motor while avoiding demagnetization of the synchronous motor.

[0049] The tolerance value of the maximum current varies depending on the temperature of the magnet used with the synchronous motor. Thus, the higher the magnet temperature, the lower the tolerance value can be.

[0050] A first modification of the synchronous motor control device according to the fifth embodiment of the present invention will now be described. The first modification is characterized in that, upon receiving the electrodynamic braking signal, the current command generation unit 1 controls the q-phase current command to decrease the q-phase current and also controls the d-phase current command to increase the d-phase current.

[0051] According to the first modification to the control device of the synchronous motor according to the fifth embodiment of the present invention, it is the same as the first modification to the control device of the synchronous motor according to the third embodiment of the present invention, which is implemented using Fig. 11, it is possible to increase the d-phase voltage and the q-phase voltage immediately before the electrodynamic braking action by increasing the d-phase current I d to reduce.

[0052] Now, a second modification of the control device of the synchronous motor according to the fifth embodiment of the present invention will be described. The second modification is characterized in that the current command generation unit, upon receiving the electrodynamic braking signal, controls the d-phase current command and the q-phase current command so that the phase of the current flowing through each of the U-phase, the V-phase, and the W-phase is changed in such a direction that the amplitude of the voltage across the terminals of the synchronous motor is reduced. In the second modification, there is such a configuration that by shifting the phase of the current, the q-phase current I q is reduced and the d-phase current I d is increased, and the electrodynamic braking action is started after confirming that the q-phase current I q the pre-defined threshold I qthhas been achieved; this can produce an effect similar to that of the first variation.

[0053] As described above, according to the control device of the synchronous motor according to the fifth embodiment of the present invention, by providing the peak current estimation unit, the peak d-phase current is continuously estimated after the start of the electrodynamic braking operation, so that it is possible to cause a rapid stop of the synchronous motor while avoiding demagnetization of the synchronous motor. [Sixth Embodiment]

[0054] Now, a control device of a synchronous motor according to a sixth embodiment of the present invention will be described using the drawings. Fig. 14 is a block diagram of the control device of the synchronous motor according to the sixth embodiment of the present invention. As shown in Fig. As illustrated in Figure 14, the control device 104 of the synchronous motor according to the sixth embodiment of the present invention includes a voltage command generation unit 5 for generating a d-phase voltage command and a q-phase voltage command; a current detection unit 2 for detecting a d-phase current and a q-phase current; a short-circuit device 3 for short-circuiting a synchronous motor 60 to electrodynamically brake the synchronous motor; a short-circuit control unit 4 for controlling the short-circuit device 3; and a peak current estimation unit 6 for continuously estimating the peak d-phase current based on the detected q-phase current. The voltage command generation unit 5 controls the d-phase voltage command and the q-phase voltage command upon receiving an electrodynamic braking signal.and the short-circuit control unit 4, after receiving the electrodynamic braking signal and after the highest estimated current after electrodynamic braking estimated by the maximum current estimation unit 6 has become less than or equal to a tolerance value, controls the short-circuit unit 3 so that the synchronous motor 60 is short-circuited.;

[0055] The control device 104 of the synchronous motor 104 according to the sixth embodiment is different from the control device 102 of the synchronous motor according to the second embodiment shown in Fig. 9, in that it further includes the maximum current estimation unit 6 that continuously estimates the maximum d-phase current based on the detected q-phase current, and that the short-circuit control unit 4, after receiving the electrodynamic braking signal and after the maximum estimated current after electrodynamic braking estimated by the maximum current estimation unit 6 becomes less than or equal to a tolerance value, controls the short-circuit unit 3 to short-circuit the synchronous motor 60. The other configuration of the synchronous motor control device 104 according to the sixth embodiment is the same as that of the synchronous motor control device 102 according to the second embodiment, and therefore, a detailed description thereof will be omitted.

[0056] According to the control device of the synchronous motor according to the sixth embodiment of the present invention, as in the control device of the synchronous motor according to the fifth embodiment, by providing the peak current estimation unit, the peak d-phase current is continuously estimated after the start of the electrodynamic braking operation, so that it is possible to cause a rapid stop of the synchronous motor while avoiding demagnetization of the synchronous motor.

[0057] Now, the d-phase current and the q-phase current in a transient state after the electrodynamic braking action will be described. In Fig. Figure 15 shows a view illustrating voltage vectors on the dq coordinates when the transient state after the electrodynamic braking action is taken into account. Fig.In Figure 15, the effective value of the coefficient for sin ωt is indicated on the horizontal axis, and the effective value of the coefficient for cos ωt is indicated on the vertical axis. Then, the voltage across the terminals of the synchronous motor is represented by equation (1) as follows: 2(Kvω+RIq+Lq⋅dIqdt−LdIdω)sinωt+2(RId+LqIqω+Ld⋅dIddt)cosωt

[0058] After the electrodynamic braking action, the voltage across the terminals is always 0 [V]; therefore, the following equations (2) and (3) apply: Kvω+RIq+Lq⋅dIqdt−LdIdω=0 RId+LqIqω+Ld⋅dIddt=0

[0059] By rewriting the above equations (2) and (3), the following equations (4) and (5) can be obtained: dIqdt=1Lq(−Kvω−RIq+LdIdω) dIddt=1Ld(−RId−LqIqω)

[0060] If Δt is small, the following equations (6) and (7) apply: Iq(t+Δt)=Iq(t)+dIqdt⋅Δt Id(t+Δt)=Id(t)+dIddt⋅Δt

[0061] Therefore, the following equations (8) and (9) can be obtained: Iq(t+Δt)=Iq(t)+1Lq(−Kvω=RIq+LdIdω)Δt Id(t+Δt)=Id(t)+1Ld(−RId−LqIqω)Δt

[0062] Using the above equations (8) and (9), it is possible to calculate the d-phase current and the q-phase current in the transient state after the electrodynamic braking action.

[0063] As described above, according to the control device of the synchronous motor of the present invention, it is possible to perform the electrodynamic braking action while avoiding demagnetization of the synchronous motor without excessively limiting the torque.

Claims

[1] Control device (101, 102, 103, 104) of a synchronous motor (60), comprising: a current command generation unit (1) for generating a d-phase current command (I d *) and a q-phase current command (I q *) to generate; a current detection unit (2) for detecting a d-phase current (I d ) and a q-phase current (I q ) to detect; a short-circuit device (3) for short-circuiting the synchronous motor (60) in order to electrodynamically brake the synchronous motor (60); and a short-circuit control unit (4) for controlling the short-circuit device (3), which receives an electrodynamic brake signal, a rotational speed (ω), a speed command (ω*), the d-phase current (I d ) and q-phase current (I q ) and the d-phase current command (I d *) and q-phase current command (I q*), receives, wherein the short-circuit device (3) is provided between an inverter (40) and the synchronous motor (60) and short-circuits terminals of the synchronous motor (60) according to a signal S of the short-circuit control unit (4), wherein the current command generation unit (1) upon receipt of the electrodynamic braking signal generates the q-phase current command (I q *) so that the q-phase current (I q ) is reduced, wherein the short-circuit control unit (4) after receiving the electrodynamic braking signal and after a predetermined time has elapsed from the control of the q-phase current command (I q *) the current command generating unit (1) controls the short-circuit device (3) so that the synchronous motor (60) is short-circuited, and wherein the current command generation unit (1) upon receipt of the electrodynamic braking signal generates the q-phase current command (I q*) so that the q-phase current (I q ) is reduced, and the d-phase current command (I d *) so that the d-phase current (I d ) is increased. [2] Control device (101, 102, 103, 104) of a synchronous motor (60), comprising: a current command generation unit (1) for generating a d-phase current command (I d *) and a q-phase current command (I q *) to generate; a current detection unit (2) for detecting a d-phase current (I d ) and a q-phase current (I q ) to detect; a short-circuit device (3) for short-circuiting the synchronous motor (60) in order to electrodynamically brake the synchronous motor (60); and a short-circuit control unit (4) for controlling the short-circuit device (3), which receives an electrodynamic brake signal, a rotational speed (ω), a speed command (ω*), the d-phase current (I d ) and q-phase current (I q ) and the d-phase current command (I d *) and q-phase current command (I q *) receives, wherein the short-circuit device (3) is provided between an inverter (40) and the synchronous motor (60) and short-circuits terminals of the synchronous motor (60) according to a signal S of the short-circuit control unit (4), wherein the current command generation unit (1) upon receipt of the electrodynamic braking signal generates the q-phase current command (I q *) so that the q-phase current (I q ) is reduced, wherein the short-circuit control unit (4) after receiving the electrodynamic braking signal and after a predetermined time has elapsed from the control of the q-phase current command (I q *) the current command generating unit (1) controls the short-circuit device (3) so that the synchronous motor (60) is short-circuited, and wherein the current command generation unit (1) upon receipt of the electrodynamic braking signal generates the d-phase current command (I d *) and the q-phase current command (I q *) controls such that a phase of a current flowing through each of a U-phase, a V-phase and a W-phase is changed in such a direction that an amplitude of a voltage across terminals of the synchronous motor (60) is reduced. [3] Control device (101, 102, 103, 104) of a synchronous motor (60), comprising: a voltage command generation unit (5) for generating a d-phase voltage command (V d*) and a q-phase voltage command (V q *) to generate; a current detection unit (2) for detecting a d-phase current (I d ) and a q-phase current (I q ) to detect; a short-circuit device (3) for short-circuiting the synchronous motor (60) in order to electrodynamically brake the synchronous motor (60); and a short-circuit control unit (4) for controlling the short-circuit device (3), which receives an electrodynamic brake signal, a rotational speed (ω), a speed command (ω*), a d-phase current command (I d *), a q-phase current command (I q *) and the d-phase current (I d ) and q-phase current (I q ) receives, wherein the short-circuit device (3) is provided between an inverter (40) and the synchronous motor (60) and short-circuits terminals of the synchronous motor (60) according to a signal S of the short-circuit control unit (4), wherein the voltage command generation unit (5) upon receipt of the electrodynamic braking signal generates the d-phase voltage command (V d *) and the q-phase voltage command (V q *) controls, and wherein the short-circuit control unit (4) after receiving the electrodynamic braking signal and after a predetermined time has elapsed from the control of the d-phase voltage command (V d *) and the q-phase voltage command (V q *) the voltage command generating unit controls the short-circuit device (3) so that the synchronous motor (60) is short-circuited. [4] Control device (101, 102, 103, 104) of a synchronous motor (60), comprising: a current command generation unit (1) for generating a d-phase current command (I d *) and a q-phase current command (I q *) to generate; a current detection unit (2) for detecting a d-phase current (I d ) and a q-phase current (I q ) to detect; a short-circuit device (3) for short-circuiting the synchronous motor (60) in order to electrodynamically brake the synchronous motor (60); and a short-circuit control unit (4) for controlling the short-circuit device (3), which receives an electrodynamic brake signal, a rotational speed (ω), a speed command (ω*), the d-phase current (I d ) and q-phase current (I q ) and the d-phase current command (I d *) and q-phase current command (I q *) receives, wherein the short-circuit device (3) is provided between an inverter (40) and the synchronous motor (60) and short-circuits terminals of the synchronous motor (60) according to a signal S of the short-circuit control unit (4), wherein the current command generation unit (1) upon receipt of the electrodynamic braking signal generates the q-phase current command (I q *) so that the q-phase current (I q ) is reduced, and wherein the short-circuit control unit (4) after receiving the electrodynamic braking signal and after the q-phase current (I q ) has reached a predetermined value, the short-circuit device (3) controls such that the synchronous motor (60) is short-circuited. [5] Control device (101, 102, 103, 104) of the synchronous motor (60) according to claim 4, wherein the current command generation unit (1) after receiving the electrodynamic braking signal, generates the q-phase current command (I q*) so that the q-phase current (I q ) is reduced, and the d-phase current command (I d *) so that the d-phase current (I d ) is increased, and wherein the short-circuit control unit (4) after receiving the electrodynamic braking signal and after at least one of the q-phase current (I q ) and the d-phase current (I d ) has reached a corresponding predetermined value, the short-circuit device (3) controls such that the synchronous motor (60) is short-circuited. [6] Control device (101, 102, 103, 104) of the synchronous motor (60) according to claim 4, wherein the current command generation unit (1) upon receipt of the electrodynamic braking signal generates the d-phase current command (I d *) and the q-phase current command (I q*) controls such that a phase of a current flowing through each of a U-phase, a V-phase and a W-phase is changed in such a direction that an amplitude of a voltage across terminals of the synchronous motor (60) is reduced, and wherein the short-circuit control unit (4) after receiving the electrodynamic braking signal and after at least one of the q-phase current (I q ) and the d-phase current (I d ) has reached a corresponding predetermined value, the short-circuit device (3) controls such that the synchronous motor (60) is short-circuited. [7] Control device (101, 102, 103, 104) of a synchronous motor (60), comprising: a voltage command generation unit (5) for generating a d-phase voltage command (V d *) and a q-phase voltage command (V q *) to generate; a current detection unit (2) for detecting a d-phase current (I d ) and a q-phase current (Iq ) to detect; a short-circuit device (3) for short-circuiting the synchronous motor (60) in order to electrodynamically brake the synchronous motor (60); and a short-circuit control unit (4) for controlling the short-circuit device (3), which receives an electrodynamic brake signal, a rotational speed (ω), a speed command (ω*), a d-phase current command (I d *), a q-phase current command (I q *) and the d-phase current (I d ) and q-phase current (I q ) receives, wherein the short-circuit device (3) is provided between an inverter (40) and the synchronous motor (60) and short-circuits terminals of the synchronous motor (60) according to a signal S of the short-circuit control unit (4), wherein the voltage command generating unit (5) upon receipt of the electrodynamic braking signal generates the d-phase voltage command (V d*) and the q-phase voltage command (V q *) controls, and wherein the short-circuit control unit (4) after receiving the electrodynamic braking signal and after at least one of a q-phase voltage (V q ) and a d-phase voltage (V d ) has reached a predetermined value, the short-circuit device (3) controls such that the synchronous motor (60) is short-circuited. [8] Control device (101, 102, 103, 104) of a synchronous motor (60), comprising: a current command generation unit (1) for generating a d-phase current command (I d *) and a q-phase current command (I q *) to generate; a current detection unit (2) for detecting a d-phase current (I d ) and a q-phase current (I q ) to detect; a short-circuit device (3) for short-circuiting the synchronous motor (60) in order to electrodynamically brake the synchronous motor (60); a short-circuit control unit (4) for controlling the short-circuit device (3), which receives an electrodynamic braking signal, a rotational speed (ω), a speed command (ω*), a highest estimated value for the d-phase current (I d ), the d-phase current (I d ) and q-phase current (I q ) and the d-phase current command (I d *) and q-phase current command (I q *) receives, wherein the short-circuit device (3) is provided between an inverter (40) and the synchronous motor (60) and short-circuits terminals of the synchronous motor (60) according to a signal S of the short-circuit control unit (4), and a maximum current estimation unit (6) to calculate, based on the detected values ​​for the d-phase current (I d ) and the q-phase current (I q ) continuously the highest value for the d-phase current (Id ) during a transient state of electrodynamic braking, wherein the current command generation unit (1) upon receipt of the electrodynamic braking signal generates the q-phase current command (I q *) so that the q-phase current (I q ) is reduced, and wherein the short-circuit control unit (4), after receiving the electrodynamic braking signal and after the highest estimated current after an electrodynamic braking operation, which is estimated by the maximum current estimation unit, has become less than or equal to a tolerance value, controls the short-circuit device (3) so that the synchronous motor (60) is short-circuited. [9] The control device (101, 102, 103, 104) of the synchronous motor (60) according to claim 8, wherein the current command generation unit (1) after receiving the electrodynamic braking signal generates the q-phase current command (I q*) so that the q-phase current (I q ) is reduced, and the d-phase current command (I d *) so that the d-phase current (I d ) is increased. [10] The control device (101, 102, 103, 104) of the synchronous motor (60) according to claim 8, wherein the current command generation unit (1) generates the d-phase current command (I d *) and the q-phase current command (I q *) controls such that a phase of a current flowing through each of a U-phase, a V-phase and a W-phase is changed in such a direction that an amplitude of a voltage across terminals of the synchronous motor (60) is reduced. [11] Control device (101, 102, 103, 104) of a synchronous motor (60), comprising: a voltage command generation unit (5) for generating a d-phase voltage command (V d *) and a q-phase voltage command (V q *) to generate; a current detection unit (2) for detecting a d-phase current (I d ) and a q-phase current (I q ) to detect; a short-circuit device (3) for short-circuiting the synchronous motor (60) in order to electrodynamically brake the synchronous motor (60); a short-circuit control unit (4) for controlling the short-circuit device (3), which receives an electrodynamic brake signal, a rotational speed (ω), a speed command (ω*), a d-phase current command (I d *), a q-phase current command (I q *), a highest estimated value for the d-phase current (I d ) and the d-phase current (I d ) and q-phase current (I q ) receives, wherein the short-circuit device (3) is provided between an inverter (40) and the synchronous motor (60) and short-circuits terminals of the synchronous motor (60) according to a signal S of the short-circuit control unit (4), and a maximum current estimation unit (6) to calculate, based on the detected values ​​for the d-phase current (I d ) and the q-phase current (I q ) continuously a highest value for the d-phase current (I d ) during a transient state of electrodynamic braking, wherein the voltage command generation unit (5) upon receipt of the electrodynamic braking signal generates the d-phase voltage command (V d *) and the q-phase voltage command (V q *) controls, and wherein the short-circuit control unit (4), after receiving the electrodynamic braking signal and after the highest estimated current after an electrodynamic braking operation, which is estimated by the maximum current estimation unit (6), has become less than or equal to a tolerance value, controls the short-circuit device (3) so that the synchronous motor (60) is short-circuited.

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